PNG 圧縮
「PNG 圧縮」は画像とデザインに使えるブラウザツールです。入力内容と結果は通常この端末内で処理され、登録は必要ありません。
EXPLICIT PNG CANDIDATES
Make a PNG candidate, then compare the bytes
Canvas has no standard PNG quality slider. Keep the original pixel dimensions and decoded RGB detail for a plain re-encode, or choose explicit resize and color-detail changes. The page never promises a smaller result.
使い方
使い方
- Choose one PNG up to 20 MB and 40 megapixels.
- Keep its dimensions and decoded RGB detail, or deliberately set a smaller longest side or fewer RGB bits.
- Create a PNG candidate, compare bytes and dimensions with the original, then download only if it suits your use.
What the browser can honestly do with PNG
Canvas can decode an image and encode a new PNG, but its PNG encoder has no standard quality control. A same-size 8-bit candidate is a fresh encoding of the browser-decoded pixels, not a guaranteed optimizer or a byte-for-byte lossless rewrite of the original file. It can be larger, especially when the source was already well optimized.
Optional changes that can reduce bytes
Lowering the longest side removes pixels. Choosing 6, 5, or 4 RGB bits per channel rounds each decoded red, green, and blue channel to fewer levels; this is visibly lossy on some artwork. Alpha values are copied from the decoded image, so transparent and semi-transparent pixels remain transparent, although color under fully transparent pixels may differ after decoding and re-encoding.
Boundaries and metadata
Input is one PNG up to 20 MB and 40 megapixels. Output is limited to 10,000 pixels per side and 40 megapixels. The browser writes a new PNG from decoded pixels; it does not preserve original metadata, color-profile chunks, animation, or exact compressed data. The selected image stays in this browser.
よくある質問
あわせて知りたいこと
Is this lossless PNG compression?
Only in a limited visual sense when you keep the original dimensions and 8 RGB bits: the page re-encodes browser-decoded pixels without deliberately changing RGB values. It does not preserve original PNG bytes, metadata, profiles, or every invisible color value, and it cannot promise a smaller file. Resizing or fewer RGB bits are lossy.
Why is there no quality slider?
The browser Canvas PNG encoder does not define a portable PNG quality setting. Presenting one would imply control the page does not have. Use the explicit size and RGB-detail controls instead.
Will transparency survive?
The candidate is encoded as PNG and copies alpha values from the decoded canvas, so ordinary transparent and semi-transparent areas remain supported. Canvas conversion does not retain original PNG metadata or color-profile chunks.
Can the result be larger?
Yes. PNG compression depends on the image content and encoder. The page compares original and candidate bytes so you can keep the original when the candidate is not useful.